THIS ultra violent psychological serial killer thriller is another version of the current, unappetising vogue for 'torture porn'.

Think Seven crossed with Saw and Hostel.

Stellan Skarsgard (Breaking the Waves) plays Eddie Argo, a detective trailing a series of brutal murders with new partner Helen Westcott (Melissa George).

Each victim has a loved one who was offered the choice of self-sacrifice.

A back story involves a gang who were the prime suspects in an horrific case in which Jean Lerner (Selma Blair) was tortured until she told the beasts to shoot her mother.

Pronounced 'Was', this unpleasant film was named after 'W delta Z' - a mathematical expression of selflessness formulated by American population geneticist George R Price.

It echoes Skarsgard's superior thriller Insomnia by almost never coming out of daylight and has two unlikely twists lurking in the shadows. But it's the viewers who will be the chief victims of debut director Tom Shankland's appetite for pain.